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Abstract:

A gas turbine configured to prevent eccentricity of a rotor (14) due to
heat is installed with a strut (23), an outer diffuser (24), an inner
diffuser (25), a strut cover (26), and a partition wall (28), wherein the
gas turbine includes an inflow hole (31) for cooling air (W), a first
flow passage (R1) formed between a casing wall (21) and the outer
diffuser (24), a second flow passage (R2) formed between the strut (23)
and the strut cover (26), a third flow passage (R3) formed between the
inner diffuser (25) and the partition wall (28), and an outflow hole (51)
installed in the inner diffuser (25).

Claims:

1. A gas turbine comprising: a casing wall having a cylindrical shape
centered at an axis and forming an outer shape of an exhaust chamber; a
bearing case disposed inside the casing wall in a radial direction and
supporting a bearing of a rotor; a plurality of struts installed on an
outer circumferential surface of the bearing case at predetermined
intervals in a circumferential direction of the bearing case and
connecting the casing wall to the bearing case; an outer diffuser
installed along an inner circumferential surface of the casing wall; an
inner diffuser installed along the outer circumferential surface of the
bearing case; a strut cover connecting the outer diffuser to the inner
diffuser and covering the strut from an outer circumference side of the
strut; and a partition wall installed between the inner diffuser and the
bearing case and covering the bearing case from an outer circumference
side of the bearing case, wherein the gas turbine comprises: an inflow
hole installed in the casing wall and taking cooling air into the casing
wall from the outside; a first flow passage formed between the casing
wall and the outer diffuser and communicated with the inflow hole to
allow the cooling air to flow therethrough; a second flow passage formed
between the strut and the strut cover and communicated with the first
flow passage to allow the cooling air to flow therethrough; a third flow
passage formed between the inner diffuser and the partition wall and
communicated with the second flow passage to allow the cooling air to
flow therethrough; and a flow rate adjustment device installed in at
least one of the second flow passage and the third flow passage.

2. The gas turbine according to claim 1, wherein the flow rate adjustment
device is an orifice member installed in the second flow passage,
protruding from an inner circumferential surface of the strut cover, and
installed between the strut cover and the strut.

3. The gas turbine according to claim 1, wherein the flow rate adjustment
device is an outflow hole installed at a downstream side in a flow
direction of the cooling air in an axial direction of the third flow
passage.

4. The gas turbine according to claim 2, wherein the flow rate adjustment
device is an outflow hole installed at a downstream side in a flow
direction of the cooling air in an axial direction of the third flow
passage.

5. The gas turbine according to claim 1, wherein the inflow hole has a
cover member capable of changing an opening area of the inflow hole.

6. The gas turbine according to claim 2, wherein the inflow hole has a
cover member capable of changing an opening area of the inflow hole.

7. The gas turbine according to claim 3, wherein the inflow hole has a
cover member capable of changing an opening area of the inflow hole.

8. The gas turbine according to claim 4, wherein the inflow hole has a
cover member capable of changing an opening area of the inflow hole.

9. The gas turbine according to claim 3, wherein the outflow hole is
disposed at an upstream side relative to the strut cover in a flow
direction of a combustion gas in an axial direction of the diffuser.

10. The gas turbine according to claim 4, wherein the outflow hole is
disposed at an upstream side relative to the strut cover in a flow
direction of a combustion gas in an axial direction of the diffuser.

Description:

TECHNICAL FIELD

[0001] The present invention relates to a gas turbine installed with a
cooling structure installed in an exhaust chamber.

[0002] This application claims priority to and the benefit of Japanese
Patent Application No. 2011-197076 filed on Sep. 9, 2011, the disclosure
of which is incorporated by reference herein.

BACKGROUND ART

[0003] A gas turbine can generate a rotational power by driving a turbine
with a high-temperature, high-pressure combustion gas which is produced
by combustion of a fuel gas and compressed air supplied into a combustor.
The combustion gas having driven the turbine is discharged to the
atmosphere after conversion of dynamic pressure into a static pressure in
a diffuser of an exhaust chamber.

[0004] In such a gas turbine, the temperature of the combustion gas
supplied to the turbine is very high due to increased efficiency.
Therefore, cooling is performed on almost all components of the turbine,
and it is also necessary to reliably cool inside of the exhaust chamber.

[0005] The above-mentioned gas turbine having a cooling structure in the
exhaust chamber is disclosed in, for example, Patent Document 1, in which
the exhaust chamber of the gas turbine is installed with a casing wall
and struts. The strut is arranged in plurality in a circumferential
direction at predetermined intervals, and connected to a bearing case
which is disposed inside the casing wall in a radial direction and houses
a bearing supporting a rotor, and supports the bearing case on the casing
wall. By supplying cooling air into the exhaust chamber through a cooling
flow passage which is formed between the strut and the strut cover
installed in an outer circumferential side of the strut, cooling of the
components in the exhaust chamber, such as the diffuser, the strut, and
the strut cover is performed.

[0007] In the exhaust chamber of the gas turbine according to the
above-mentioned related art, almost all of the components are
manufactured by sheet metal welding, and a manufacturing dimensional
tolerance is large also in the struts disposed in the circumferential
direction. As a result, a difference in cooling effect occurs due to a
difference in flow rate of the cooling air supplied through the cooling
flow passage, resulting in a difference in amounts of thermal expansion
of the components in the exhaust chamber. Accordingly, in the strut in
particular, there has been a risk of contact between a rotary body and a
stationary body, and performance degradation of the gas turbine caused by
eccentricity between the bearing case and the rotor due to a difference
in the amount of thermal expansion of the respective struts in the
circumferential direction.

[0008] The present invention has been made in view of the above-mentioned
circumstances, an object of which is to provide a gas turbine capable of
preventing eccentricity of a rotor.

Means for Carrying out the Invention

[0009] In order to solve the problems, the present invention employs the
following means.

[0010] A gas turbine according to the present invention includes: a casing
wall having a cylindrical shape centered at an axis and forming an outer
shape of an exhaust chamber; a bearing case disposed inside the casing
wall in a radial direction and supporting a bearing of a rotor; a
plurality of struts installed on an outer circumferential surface of the
bearing case at predetermined intervals in a circumferential direction of
the bearing case and connecting the casing wall to the bearing case; an
outer diffuser installed along an inner circumferential surface of the
casing wall; an inner diffuser installed along the outer circumferential
surface of the bearing case; a strut cover connecting the outer diffuser
to the inner diffuser and covering the strut from an outer circumference
side of the strut; and a partition wall installed between the inner
diffuser and the bearing case and covering the bearing case from an outer
circumference side of the bearing case, wherein the gas turbine includes:
an inflow hole installed in the casing wall and taking in cooling air
from the outside; a first flow passage formed between the casing wall and
the outer diffuser and communicated with the inflow hole to allow the
cooling air to flow therethrough; a second flow passage formed between
the strut and the strut cover and communicated with the first flow
passage to allow the cooling air to flow therethrough; a third flow
passage formed between the inner diffuser and the partition wall and
communicated with the second flow passage to allow the cooling air to
flow therethrough; and a flow rate adjustment device installed in at
least one of the second flow passage and the third flow passage.

[0011] In the gas turbine, the cooling air is taken in from the inflow
hole and flows through the first flow passage, the second flow passage
and the third flow passage. Thereafter, the cooling air cools the casing
wall, the outer diffuser, the strut, the strut cover, the inner diffuser
and the partition wall, which are components of the exhaust chamber,
before flowing out into a combustion gas in a diffuser part surrounded by
the outer diffuser and the inner diffuser. Here, the flow rate of the
cooling air taken in from the inflow hole is adjusted by the flow rate
adjustment device. This allows the cooling air to flow at the same flow
rate in the circumferential direction, even when dimensions of the first
flow passage, the second flow passage and the third flow passage are
non-uniform in the circumferential direction due to manufacturing
dimensional tolerance of the components. As a result, the amount of
thermal expansion of all the struts can be uniformized.

[0012] Further, the flow rate adjustment device may be an orifice member
which is disposed in the second flow passage so as to protrude from an
inner circumferential surface of the strut cover, and has an orifice
installed between the strut cover and the strut.

[0013] By providing the orifice member having the orifice at the second
flow passage, a flow passage area between all of the struts and strut
covers in the circumferential direction can be made constant regardless
of the manufacturing dimensional tolerance of the respective struts and
strut covers. Thereby it is possible to adjust the cooling air flowing
through the entire second flow passage to the same flow rate, and avoid
non-uniformization of the cooling effect to the respective struts.
Accordingly, eccentricity of a rotor caused by deviation in the amount of
thermal expansion of the respective struts can be prevented. As a result,
contact between a rotary body and stationary body can be prevented and
performance of the gas turbine can be improved.

[0014] Further, the flow rate adjustment device may be an outflow hole
which is installed at a downstream side in a flow direction of the
cooling air of the third flow passage in an axial direction of the
diffuser.

[0015] The cooling air having flowed through the respective second flow
passages in the circumferential direction joins as one in the third flow
passage, i.e., at the upstream of the outflow hole. Meanwhile, in an
inlet of the diffuser part through which a combustion gas leaving a final
stage blade is discharged, the pressure varies widely, and the pressure
distribution in the circumferential direction is likely to occur. When
the outflow hole is installed at the downstream side of the third flow
passage in the flow direction of the cooling air in the axial direction
of the diffuser, the outflow hole functions as a throttling section of a
cooling air flow. Accordingly, pressure loss is applied to the cooling
air flow, so that non-uniformity of the pressure distribution in the
circumferential direction in the chamber forming the third flow passage
can be reduced. The flow rate of the cooling air flowing through each of
the second flow passages in the circumferential direction is determined
by the pressure difference between the pressure in the third flow passage
and the pressure outside the inflow hole. Therefore, by uniformizing
pressure distribution in the circumferential direction, it is possible to
reduce non-uniformaization of the flow rate of the cooling air flowing
through the respective second flow passages in the circumferential
direction, and prevent eccentricity of the rotor due to deviation in
amount of thermal expansion of the respective struts.

[0016] In addition, the inflow hole may have a cover member capable of
changing an opening area of the inflow hole.

[0017] Since access to the inflow hole from the outside is easy,
adjustment of an intake amount of the cooling air from the outside can be
performed by the cover member, and a total flow rate of the cooling air
flowing into the exhaust chamber can be easily adjusted to an arbitrary
flow rate. Accordingly, the cooling amount of the components can be
easily adjusted.

[0018] In addition, the outflow hole may be disposed at an upstream side
of the strut cover in a flow direction of a combustion gas in an axial
direction of the diffuser.

[0019] At the upstream side in the flow direction of the combustion gas in
the axial direction of the gas turbine, a negative pressure with respect
to a static pressure is larger in comparison with the downstream side in
the flow direction of the combustion gas in the axial direction of the
diffuser. For this reason, when the cooling air is taken in by the
pressure difference, a large amount of cooling air can be more smoothly
taken in, and a higher cooling effect to the components can be obtained.

Effects of the Invention

[0020] According to the gas turbine of the present invention, the cooling
air is uniformly discharged by the flow rate adjustment device into the
diffuser part surrounded by the outer diffuser and the inner diffuser in
the circumferential direction, so that an amount of thermal expansion of
each strut can be uniformized, and eccentricity of the rotor can be
prevented.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] FIG. 1 is a schematic view of a gas turbine according to a first
embodiment of the present invention.

[0022] FIG. 2 is an enlarged view showing a strut installation portion of
an exhaust chamber.

[0023] FIG. 3 is a view showing the strut installation portion of the
exhaust chamber when seen in an axial direction thereof.

[0024]FIG. 4 is an enlarged view showing an inflow hole and a cover in a
casing wall of the exhaust chamber.

[0025] FIG. 5A is a view showing an orifice in a strut cover.

[0026] FIG. 5B is a cross-sectional view taken along line A-A of FIG. 5A,
showing the orifice in the strut cover.

[0027] FIG. 6 is a cross-sectional view taken along line A-A of FIG. 2,
schematically showing relation between the inflow hole and the orifice
and between the chamber and an outflow hole.

MODES FOR CARRYING OUT THE INVENTION

[0028] Hereinafter, a gas turbine 1 according to a first embodiment of the
present invention will be described.

[0029] As shown in FIG. 1, the gas turbine 1 is configured to generate a
high temperature, high pressure combustion gas W1 by combusting
compressed air produced in a compressor 11 after mixing with a fuel in a
combustor 12. In addition, the turbine obtain rotational power by forcing
the combustion gas W1 to flow into a turbine 13, and thereby causing a
rotor 14 of the turbine 13 to rotate about an axis P. Further, the
turbine 13 is connected to, for example, a generator (not shown) to
generate power using the rotational power.

[0030] Then, the combustion gas W1 is exhausted through an exhaust chamber
15 after rotating the turbine 13.

[0031] Hereinafter, the compressor 11 side (a left side of FIG. 1) of the
gas turbine 1 is referred to as an upstream side in the direction of the
axis P, and the exhaust chamber 15 side (a right side of FIG. 1) is
referred to as a downstream side in the direction of the axis P.

[0032] As shown in FIGS. 2 and 3, the exhaust chamber 15 includes a casing
wall 21, a bearing case 22, and a strut 23. The bearing case 22 is
disposed inside the casing wall 21 in a radial direction. The strut 23
connects the casing wall 21 to the bearing case 22.

[0033] Further, the exhaust chamber 15 includes an outer diffuser 24, an
inner diffuser 25, a strut cover 26, and a partition wall 28. The outer
diffuser 24 is installed along an inner circumferential surface of the
casing wall 21. The inner diffuser 25 is installed along an outer
circumferential surface of the bearing case 22. The strut cover 26
connects the outer diffuser 24 to the inner diffuser 25 and covers a
strut outer circumference surface 23a. The partition wall 28 is installed
between the inner diffuser 25 and the bearing case 22.

[0034] The casing wall 21 is a member having a cylindrical shape about the
axis P and forming an outer shape of the exhaust chamber 15.

[0035] The bearing case 22 is a member disposed inside the casing wall 21
in a radial direction to accommodate and support a bearing 27 of the
rotor 14 and having a cylindrical shape about the axis P.

[0036] In addition, the bearing case 22 has a protrusion. The protrusion
is a portion protruding from the bearing case 22 and has a flat surface.
The surface is a surface parallel to a plane along the axis P.

[0037] A first end 23A of the two ends of the strut 23 is coupled onto an
outer circumferential surface of the bearing case 22, and a second end
23B of the strut 23 is coupled to the casing wall 21. That is, the strut
23 extends from the first end 23A outward in the radial direction to be
directed to one side around the axis P, and is installed in plurality (in
the embodiment, six) in a circumferential direction at predetermined
intervals. Thereby, the bearing case 22 and the casing wall 21 are
connected by the strut 23.

[0038] In addition, the first end 23A of the strut 23 is disposed
perpendicular to the flat surface of the protrusion of the bearing case
22. The strut 23 is installed to extend in a tangential direction of the
bearing case 22 having a cylindrical shape. While the bearing case 22
receives force in a rotational direction of the rotating rotor 14, the
strut 23 supports the bearing case 22 in a direction opposite to the
rotational direction. As a result, the bearing case 22 can be fixed
without rotating the bearing case 22 around the axis P.

[0039] The outer diffuser 24 is a partition wall installed along the inner
circumferential surface of the casing wall 21 inside in the radial
direction of the casing wall 21, and is a member having a substantially
cylindrical shape about the axis P. The strut 23 passes through the outer
diffuser 24.

[0040] The inner diffuser 25 is a partition wall installed along the outer
circumferential surface of the bearing case 22 inside the outer diffuser
24 and outside in the radial direction of the bearing case 22, and is a
member having a substantially cylindrical shape about the axis P. The
strut 23 passes through the inner diffuser 25.

[0041] The strut cover 26 is a partition wall connecting the outer
diffuser 24 to the inner diffuser 25, and is a member covering around the
strut 23 in an extension direction thereof.

[0042] The partition wall 28 is a partition wall installed between the
inner diffuser 25 and the bearing case 22, and has a substantially
cylindrical shape about the axis P. It prevents cooling air W having
flowed through a second flow passage R2 from directly entering the rotor
14 via the bearing case 22 and the bearing 27.

[0043] Next, a flow passage through which the cooling air W flows will be
described. The exhaust chamber 15 includes an inflow hole 31 of the
cooling air W, and three flow passages including a first flow passage R1,
the second flow passage R2 and a third flow passage R3 having an outflow
hole 51. The exhaust chamber 15 further includes a diffuser part 53 which
is surrounded by the outer diffuser 24 and the inner diffuser 25 and
forms an annular space through which the combustion gas W1 leaving the
turbine 13 flows.

[0044] The inflow hole 31 is an opening passing through the casing wall 21
through which the inside and the outside in the radial direction of the
casing wall 21 communicate with each other and the cooling air W from the
outside can flow in. The inflow hole 31 is installed in plurality (in the
embodiment, six) in the circumferential direction at predetermined
intervals, and each of the inflow holes 31 is disposed exactly in the
middle of the neighboring struts 23 in the circumferential direction.

[0045] Further, as shown in FIG. 4, a disc-shaped cover (a cover member)
32 is fixed to each of the inflow holes 31 by bolts 33. The cover 32
includes a net member 34, a cover main body 35, and a cover support
member 37. The cover main body 35 covers the net member 34 from the
further outside in the radial direction of the net member 34. The cover
support member 37 supports the net member 34 from the inside in the
radial direction. In the cover main body 35, a through hole 36 is
installed in plurality (in the embodiment, eight) at predetermined
intervals on a circumference having a constant radius from a center of
the cover main body 35. That is, the inside and the outside of the casing
wall 21 are in communication with each other through the through-holes
36, in a state in which the net member 34 is exposed to the outside only
through the through-holes 36.

[0046] The first flow passage R1 is formed in a space between the casing
wall 21 and the outer diffuser 24. The space and the inflow hole 31 are
in communication with each other, so that the cooling air W introduced
from the inflow hole 31 can flow through the first flow passage R1.

[0047] The second flow passage R2 is formed in a space between the strut
cover 26 and the strut 23. The space and the first flow passage R1 are in
communication with each other, so that the cooling air W introduced from
the first flow passage R1 can flow through the second flow passage R2.

[0048] The third flow passage R3 is formed in a space between the inner
diffuser 25 and the partition wall 28. The space and the second flow
passage R2 are in communication with each other, so that the cooling air
W introduced from the second flow passage R2 can flow through the third
flow passage R3.

[0049] The diffuser part 53 is an annular space surrounded by the outer
diffuser 24 and the inner diffuser 25 and into which the combustion gas
W1 from a final stage blade part 52 is introduced from a diffuser inlet
53a.

[0050] Further, as shown in FIGS. 5A, 5B, and 6, the exhaust chamber 15
includes an orifice member (a flow rate adjustment device) 61, and a
chamber 63. The orifice member (the flow rate adjustment device) 61 is
installed in the second flow passage R2, i.e., between the strut cover 26
and the strut 23. The chamber 63 is installed in the third flow passage
R3, i.e., between the inner diffuser 25 and the partition wall 28, and
has the outflow hole (a flow rate adjustment device) 51 formed at a
downstream side in a flow direction of the cooling air W.

[0051] The orifice member 61 is a member installed in the second flow
passage R2 to protrude toward the inner circumferential surface of the
strut cover 26 and having a flow passage area between the orifice member
61 and the strut 23. An orifice 61a and a strut outer circumference
surface 23a are machined so as to improve tolerance. Then, the orifice
member 61 having the same flow passage area is installed in the entire
strut cover 26 such that a flow rate of the cooling air W flowing through
the entire second flow passage R2 is uniformized. The orifice member 61
is a baffle member installed in the second flow passage R2 to reduce a
cross-sectional area of the second flow passage R2.

[0052] The chamber 63 is an annular space which forms the third flow
passage R3 and is surrounded by the inner diffuser 25 and the partition
wall 28 to communicate in the circumferential direction. The outflow hole
51 is disposed at a downstream side of the flow direction of the cooling
air W in the direction of the axis P in the chamber 63.

[0053] The outflow holes 51 are openings formed in a flow direction of the
combustion gas W1 in the direction of the axis P of the inner diffuser 25
and disposed in the diffuser inlet 53a at the upstream side at
predetermined intervals in the circumferential direction. The outflow
holes 51 allows communication between the inside of the inner diffuser 25
and the outside so that the cooling air W having passed through the third
flow passage R3 can flow into the diffuser part 53 immediately downstream
of an outlet of the final stage blade part 52 in the turbine 13.

[0054] In the above-mentioned gas turbine 1, the outside air is taken as
the cooling air W from the inflow hole 31 of the casing wall 21 to flow
into the first flow passage R1. Here, a pressure (static pressure) of the
diffuser inlet 53a through which the combustion gas W1 leaving the final
stage blade part 52 of the turbine 13 is discharged is in a negative
pressure state. The cooling air W is automatically suctioned from the
inflow hole 31 and taken into the diffuser part 53 due to its negative
pressure. Then, the casing wall 21 and the outer diffuser 24 are cooled
by the cooling air W while it flows through the first flow passage R1.

[0055] Thereafter, in the cooling air W having flowed into each of the
second flow passages R2 in the circumferential direction, a constant
pressure difference is secured in the cooling air W between the upstream
side and the downstream side of the orifice member 61 in the entire
second flow passage R2 by the orifice member 61 installed in the strut
cover 26, so that a flow rate of the cooling air W is adjusted.
Accordingly, non-uniformization of the flow rate of the cooling air W
flowing through the respective second flow passages R2 in the
circumferential direction can be suppressed.

[0056] Then, a flow rate of the cooling air W flowing through the
respective second flow passages R2 in the circumferential direction is
adjusted by the orifice member 61, and the cooling air W cools the strut
cover 26 and the strut 23 before flowing into the third flow passage R3.

[0057] In the third flow passage R3, the inner diffuser 25 and the
partition wall 28 are cooled by the cooling air.

[0058] Here, the flow rate of the cooling air W flowing through the
respective second flow passages R2 in the circumferential direction is
determined by a pressure difference between the pressure in the third
flow passage R3 and the pressure in the first flow passage R1. Meanwhile,
the cooling air W in the third flow passage R3 is blown to the diffuser
inlet 53a of the diffuser part 53 in which the combustion gas W1 flows
downward. The diffuser inlet 53a is disposed at a position at which the
combustion gas W1 leaving the final stage blade part 52 flows out and the
pressure distribution in the circumferential direction is non-uniform.

[0059] In addition, for normal function of the orifice member 61 installed
in the second flow passage R2, it is necessary to stabilize the pressure
difference of the cooling air W between the upstream side and the
downstream side of the orifice member 61, and stabilize a pressure
(static pressure) in the third flow passage R3.

[0060] In the diffuser inlet 53a through which the cooling air W blows
out, as described above, the pressure distribution in the circumferential
direction is non-uniform, and the pressure varies widely. For this
reason, the outflow hole 51 which functions as a throttling section is
annularly installed at a downstream side of the third flow passage R3 in
the flow direction of the cooling air W in the direction of the axis P.
By applying pressure loss sufficient for absorbing the pressure variation
in the circumferential direction of the diffuser inlet 53a to the cooling
air W blowing out from the outflow hole 51, the pressure in the
circumferential direction of the third flow passage R3 can be stabilized
without being affected by the pressure variation in the diffuser part 53.

[0061] As the pressure in the circumferential direction of the third flow
passage R3 is stabilized, a pressure difference of the cooling air W
between the upstream side and the downstream side flowing through the
orifice member 61 is stabilized. Accordingly, it is possible to reduce
non-uniformization of the flow rate of the cooling air W flowing through
the respective second flow passages R2 in the circumferential direction,
and thereby reduce deviation in the amount of thermal expansion of the
respective struts 23 can be reduced.

[0062] It is preferable that the chamber 63 has a sufficient capacity in
comparison with a total amount of the cooling air W flowing from the
inflow hole 31 and flowing around the strut 23. When the capacity of the
chamber 63 is larger in comparison with the flow rate of the cooling air
W, a constant pressure can be maintained in the chamber 63 even when the
flow rate of the cooling air W is varied.

[0063] While the cooling air W flows into the inflow hole 31 via the
through-hole 36 installed in the cover main body 35, introduction of
contaminants, dust, dirt, and so on can be prevented by the net member
34.

[0064] Further, at the stage of a test operation of the gas turbine, a
total flow rate of the cooling air W flowing around the strut 23 may be
adjusted as a tuning operation. In this case, a flow passage area of the
cooling air W supplied from the inflow hole 31 is adjusted. That is, the
hole diameter of the through-hole 36 installed in the cover main body 35
can be easily varied by replacing the cover main body 35 with another
cover main body 35 having a different hole diameter. By this method, the
total flow rate of the cooling air W flowing into the exhaust chamber 15
from the inflow hole 31 can be adjusted to an arbitrary value.

[0065] In addition, since the combustion gas W1 that has completed its
task in the turbine 13 recovers the pressure (a static pressure) as it
flows to the downstream side in the direction of the axis P in the
diffuser part 53, a negative pressure value with respect to the static
pressure is larger at the upstream side in the direction of the axis P.
In the embodiment, since the outflow hole 51 is installed at the upstream
side in the direction of the axis P of the inner diffuser 25, a larger
amount of the cooling air W can be smoothly taken in from the inflow hole
31 to improve a cooling effect of the components in the exhaust chamber
15.

[0066] Here, the strut 23 is connected to protrude from the bearing case
22 in a tangential direction thereof When the strut 23 is expanded and
contracted by heat, if the expansion and contraction amount by heat of
the respective struts 23 is uniform, the bearing case 22 is rotated about
the axis P, and eccentricity of the rotor 14 can be avoided.

[0067] According to the gas turbine 1 of the embodiment, the cooling air W
taken in from the inflow hole 31 can constantly maintain the flow passage
area of each of the second flow passages R2 by means of the orifice
member 61 installed at the second flow passage R2. In addition, the
pressure distribution in the circumferential direction can be uniformized
by the chamber 63 installed upstream of the outflow hole 51. As a result,
the flow rate of the cooling air W flowing through the second flow
passages R2 separated in the circumferential direction can be maintained
at the same flow rate in the entire second flow passage R2, and
non-uniformization of the cooling effect of the components in the
circumferential direction can be solved. Accordingly, the expansion and
contraction amount by heat of the respective struts 23 in the
circumferential direction can be uniformized, and eccentricity of the
rotor 14 can be suppressed by causing the bearing case 22 to rotate about
the axis P.

[0068] In addition, since the opening area of the inflow hole 31 of the
cover main body 35 can be easily varied, the total flow rate of the
cooling air W flowing into the exhaust chamber 15 can be easily adjusted
to an arbitrary flow rate. Accordingly, adjustment of the cooling amount
of the components can be easily performed.

[0069] Further, as the outflow hole 51 is installed in the diffuser inlet
53a at the upstream side in the direction of the axis P of the diffuser
part 53, the cooling air W can be smoothly introduced and the flow rate
can be increased. Accordingly, the cooling effect to the components in
the exhaust chamber 15 can be improved, leading to improved performance
of the gas turbine 1.

[0070] In addition, when the cooling air W flows from the first flow
passage R1 to pass through the third flow passage R3, the cooling air W
is heated by heat exchange between the components and the cooling air W,
and non-uniform pressure distribution may occur in the circumferential
direction in the chamber 63 due to a generated stack effect. However, as
the appropriate pressure loss (the pressure loss sufficient for the stack
effect) is applied by the above-mentioned orifice member 61, the
influence by the stack effect can be reduced to a negligible level, and
the flow rate of the cooling air W can be uniformized.

[0071] Hereinabove, while the embodiment of the present invention has been
described in detail, some design changes may be made without departing
from the technical spirit of the present invention.

[0072] For example, when the inner circumferential surface of the strut
cover 26 can be machined to maintain a constant flow rate of the cooling
air W flowing through the respective second flow passages R2 in the
circumferential direction, there is no need to provide the orifice member
61 at the second flow passage R2.

[0073] In addition, when the pressure distribution in the circumferential
direction in the third flow passage R3 upstream of the outflow hole 51 is
constant, the outflow hole 51 may be omitted.

[0074] Further, in the embodiment, while the strut 23 is installed to
protrude in the tangential direction of the bearing case 22, for example,
the strut 23 may be installed to protrude outward in the radial
direction, and the number of struts 23 is not limited to six.

[0075] Furthermore, while the cooling air W from the inflow hole 31 is
taken in by the negative pressure, the cooling air W may be taken in by
forcing in from the inflow hole 31 using a fan or the like.

[0076] Then, while the outflow hole 51 is disposed at the diffuser inlet
53a at the upstream side in the direction of the axis P of the diffuser
part 53, it may be disposed at the downstream side in the direction of
the axis P. In this case, since the negative pressure amount is smaller
in comparison with the upstream side in the direction of the axis P, an
intake amount of the cooling air W is reduced. However, the flow rate can
be adjusted by increasing the hole diameter of the inflow hole 31.